The role of the fathers is interesting as well. Charlie's served at the end of WWII, and Armstrong's father lost a leg in Korea, and this shapes the way they treat their children. There were other interesting adult characters as well-- the lonely but helpful Mr. Khalil, and the poor beleaguered aide, Edwina Gaines, who writes hysterical incident reports when things go wrong at school.
The only thing that I disliked about this was the inclusion of the brother's death, and the mother's dysfunctional way of dealing with that, but that is a personal issue. It was addressed fairly lightly in the book, and the mother does finally get her act together.
Armstrong and Charlie is a must read for middle grade students who are trying to figure out their own place in the world, since that's exactly what these characters are trying to do. They're just trying to do it in a world where there are banana seats on bicycles and peanut butter in every sandwich in the lunch room. 6th grade is still about learning to spread the Ho Hos around, and good historical fiction manages to show students that while things may change, they really stay very much the same.